With an increasing percentage of the population comprising elderly or infirm persons living alone, the demand for a means to monitor the well-being of these individuals has increased. Periodic visits by other individuals, such as visiting nurses or family members, provide a measure of security, and the telephone provides a means for summoning help in an emergency. However, many situations immediately come to mind whereby an incapacitating emergency, such as a fall, occurs between such visits and when an individual is located some distance away from their phone.
As a result of the potential for these emergency situations, a number of service businesses have organized which provide a monitoring service for people living alone. Typically, a person (called a subscriber) wishing to be monitored is supplied with a remote station, called a home communicator. The remote station links the person's home with a central monitoring station by means of a telephone. Also typically, the subscriber is provided with a small personal help button which is worn by the subscriber and which is in radio communication with the remote station. In the event of an emergency the subscriber need only press a button on the personal help button to cause the remote station to call the the central monitoring station and indicate that the subscriber requests help.
When the central monitoring station receives the help call from the subscriber, the person at the central monitoring station attempts to establish two way communication with the subscriber in order to ascertain the nature of the emergency. This is generally accomplished by incorporating a speakerphone into the remote station. Control signals, such as a tone or a sequence of tones, which are sent from the central monitoring station, control the operation of the speakerphone at the remote station. Since the telephone lines linking the central monitoring station and the remote station may vary in quality, thereby causing variability in received signal levels, the intensity of the control signals must be sufficient to cause the remote station to respond to the control signals and yet not be so intense as to cause audio annoyance during the interval between the time the speakerphone switches from the speaker mode to microphone mode.